Slug (mass)

# Slug (mass)

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The slug is a unit of mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

associated with Imperial units. It is a mass that accelerates by 1 ft/s2 when a force of one pound-force
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...

is exerted on it.

With standard gravitation gc = , the international foot of and the avoirdupois pound of , one slug therefore has a mass of approximately or . At the surface of the Earth, an object with a mass of 1 slug exerts a force of about or .

## History

The slug is part of a subset of units known as the gravitational FPS system, one of several such specialized systems of mechanical units developed in the late 19th and the 20th century. Geepound was another name for this unit in early literature.

The name "slug", as a unit of inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...

, was coined before 1900 by British physicist Arthur Mason Worthington
Arthur Mason Worthington
Arthur Mason Worthington CB, FRS was an English physicist and educator. He is best known for his work on fluid mechanics, especially the physics of splashes; for observing those, he pioneered techniques of high speed photography...

, but it did not see any significant use until decades later. A 1928 textbook says:
The slug is listed in the "Regulations under the Weights and Measures (National Standards) Act, 1960". This regulation defines the units of weights and measures, both regular and metric, in Australia.

## Similar units

The blob or slinch (a portmanteau of the words slug and inch
Inch
An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...

) is an inch version of the slug (1 slinch = 1 lbf·s2/in = 12 slugs). Slang terms for the slinch include the slugette.

Metric units include the "glug" in the centimetre-gram-second system, and the "mug", "par", or "MTE" in the metre-kilogram-second system.